Chemistry Reference
In-Depth Information
8
Biologically Controlled Mineralization
in Prokaryotes
Dennis A. Bazylinski
Department of Biochemistry, Biophysics, and Molecular Biology
Iowa State University
Ames, Iowa 50011 U.S.A.
Richard B. Frankel
Department of Physics
California Polytechnic State University
San Luis Obispo, California 93407 U.S.A.
INTRODUCTION
As stated in an Chapter 4, prokaryotes of both Domains or Superkingdoms, the
Bacteria and the Archaea, mediate the formation of a large number of diverse minerals.
They are known to do this either through biologically induced mineralization (BIM)
(Lowenstam 1981) (the subject of Chapter 4 in this volume; Frankel and Bazylinski
2003) or biologically controlled mineralization (BCM). The latter has also been referred
to as organic matrix-mediated mineralization (Lowenstam 1981) and boundary-organized
biomineralization (Mann 1986). There are several important differences between BIM
and BCM that will be discussed in detail in this chapter, most notably those dealing with
aspects of the mineral crystals and the biomineralization process (see also Weiner and
Dove 2003). However, there is another significant difference between the two modes of
biomineralization and this is the aspect of functionality. Generally, in BIM there is no
function to the biomineralized particles except, perhaps, as a solid substrate for
attachment in the case of bacteria or as a form of protection against certain environmental
conditions or attack from predators. However, it is easier to recognize the primary
function of bone or shells produced by molluscs; two well-characterized examples of
BCM by higher organisms. Functionality should always be examined when dealing with
examples of biomineralization particularly in situations where the mineral product
displays some qualities of both BIM and BCM.
In BCM, the organism exerts a great degree of crystallochemical control over the
nucleation and growth of the mineral particles. For the most part, the minerals are directly
synthesized at a specific location within or on the cell and only under certain conditions.
The mineral particles produced by bacteria in BCM are characterized as well-ordered
crystals with narrow size distributions, and specific, consistent particle morphologies.
Because of these features, BCM processes are likely to be under specific
chemical/biochemical and genetic control. In the microbial world, the most characterized
example of BCM is magnetosome formation by the magnetotactic bacteria, a group of
microorganisms in which BCM-produced magnetic crystals appear to have a relatively
specific function. There are some examples of biomineralization that appear to be
intermediate between BIM and BCM; these are covered in Chapter 4 (Frankel and
Bazylinski 2003) since the mineralization product usually has more features in common
with BIM. This chapter is, in effect, a review of the magnetotactic bacteria. However, it
should be remembered that the production of magnetic minerals by the magnetotactic
bacteria is used in this volume as an example of BCM. The microbiological, geological,
chemical, biochemical, and physical approaches used to study BCM in the magnetotactic
